The present invention relates to filters capable of removing a variety of contaminants, including pathogens, from air by filtration. The filters provide effective filtration of a broad range of contaminants at high flow rates with relatively low pressure drops. In particular, the invention encompasses filters that comprise activated carbon fibers, particularly activated carbon fiber composites, for removing a broad spectrum of contaminants, including viruses, from air. Additionally, the invention relates to a method of removing contaminants from air using those filters.
The purity of the air we breathe is critical to our health and well being. Yet, that air contains a very broad range of contaminants including, for example, particulates, harmful chemicals, organic materials, and microbiological organisms, such as bacteria, parasites, protozoa and viruses. In addition to the health needs of the general public, specific situations, such as factory floors, public waiting areas, medical and surgical suites, hospital rooms, manufacturing operations (such as for the manufacture of certain electronic components), and airplane cabins, offer particularly difficult and challenging requirements for air purification and filtration systems.
While air filtration devices have been developed to address at least some of these needs, they tend to require a trade-off between filtration efficacy/efficiency and the large, cumbersome and complex nature of the device, i.e., greater efficacy/efficiency generally requires greater complexity. Further, devices which are used to filter out particularly small components, such as biological components, because they frequently rely on very small pore size, tend to require low flow rates or have high pressure drops, thereby rendering the systems relatively inefficient. Examples of some of these prior art systems are described below.
U.S. Pat. No. 3,770,625, Wallis, et al., issued Nov. 6, 1973, describes the use of activated carbon treated with sodium hydroxide to remove viruses from fluids, such as waste water.
U.S. Pat. No. 4,828,698, Jewell, et al., issued May 9, 1989, describes a cylindrical filter having multiple separate components made from polypropylene microfibers for removing particulates, chemicals and pathogens from liquids. These filters are said to provide good flow rates during the filtration process.
U.S. Pat. No. 5,997,619, Knuth, et al., issued Dec. 7, 1999, describes an air filtration system which includes HEPA filters to remove particulates and ultraviolet irradiation to provide a germicidal effect to the filtered air.
U.S. Pat. No. 6,063,170, Deibert, issued May 16, 2000, describes an air filtration system, which includes four separate units: a prefilter to remove dust particulates, germicidal UV lamps to remove bacteria, a medicated wet filtration system for viruses, and a final carbon filter.
U.S. Pat. No. 6,119,689, Korman, issued Sep. 19, 2000, describes a personal air filtration system which uses a combination of HEPA and ULPA filters sandwiching an electrostatic filter. The system is primarily aimed at filtering out particulate materials.
There is a need for a simple filter capable of simultaneously removing a broad spectrum of contaminants from air. This filter would comprise a single small, lightweight, self-contained system rather than a complex multi-component and/or multi-stage system to remove the various contaminants. Such a filter would not only be more reliable than a complex system, but it would also be far more portable and economical. In addition, it would be efficient in its use, permitting a relatively high flow rate through the filter, as well as exhibiting a relatively low pressure drop through the filter system. This would enable the filter not only to be adopted for home use, but also in a variety of situations, such as in a factory and manufacturing context, medical and surgical contexts, and areas where large numbers of people are together for relatively long periods of time, such as hospital or doctor waiting rooms and airplane cabins. The filters of the present invention meet these needs.
Although PCT Published Application No. WO 00/04977, Jagtoyen, et al., published Feb. 3, 2000, describes carbon filters which are used to remove a variety of contaminants, including pathogens, from fluids, that application does not disclose the air filtration filters and methods of the present application, and particularly does not disclose the relatively high flow rates and the relatively small filtration paths which provide outstanding filtration of air utilizing the present invention.
The present invention relates to a process for removing contaminants, including for example, organic materials and pathogens, from air, comprising passing said air, at a flow rate of from about 3 to about 30 lpm, through a filter comprising an activated carbon fiber composite, said filter having a density of from about 0.35 to about 0.70 g/cc. Preferred filters utilized in this process have a burn-off during activation of at least about 20% and no greater than about 70%, particularly from about 40% to about 50%. Preferred filter shapes are disc filters, candle/annular filters, corrugated filters or block filters. These composite filters, when compared to an analogous filter utilizing free fibers, can provide excellent filtration of a variety of contaminants at higher flow rates and with lower pressure drops.
The present invention also encompasses a filter for removing contaminants, including for example, organic materials and pathogens, from air, comprising activated carbon fibers (preferably in the form of a composite), said filter having a density of from about 0.35 to about 0.70 g/cc, and at least one wall of said filter having a thickness of no greater than about 3 inches (preferably no greater than about 2 inches, most preferably no greater than about 1 inch), through which at least a portion of the air passes during the filtration process. Preferred filters have a burn-off during activation of at least about 20% and no greater than about 70%, most preferably between about 40% and about 50%. These filters preferably have a structure of a disc filter, a candle/annular filter, a corrugated filter, or a block filter. The filters are able to filter air effectively (removing a broad range of contaminants) through a relatively thin wall thereby allowing a higher flow rate and a lower pressure drop than other types of air filters.
Finally, the present invention encompasses a process for removing contaminants, including for example, organic materials and pathogens, from air, comprising passing said air through a filter comprising activated carbon fibers (preferably in the form of a composite), said filter having a density of from about 0.35 to about 0.70 g/cc, such that at least a portion of the air passes through a wall in said filter having a thickness of no greater than about 3 inches (preferably no greater than about 2 inches, most preferably no greater than about 1 inch).